new measures for reducing fricti on in the drive train · split at a ratio of 70 to 30 in the...

Schaeffl er SYMPOSIUM 2010

28 Reduced fricti on in the drivetrain

366 Schaeffl er SYMPOSIUM 2010 367

28Reduced fricti on in the drivetrain

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367Schaeffl er SYMPOSIUM 2010Schaeffl er SYMPOSIUM 2010366

New measures for reducing fricti on in the drive train

Robert PlankDietmar Schwarzenthal, Dr. Ing. h.c. F. Porsche AG





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SummaryIn a joint advanced development project, Dr. Ing. h.c. F. Porsche AG and Schaeffler KG developed a CO2 demonstration vehicle. New optimized com-ponents for the drive train and chassis were in-corporated in this vehicle in order to reduce the fuel consumption in the New European Driving Cycle (NEDC) by around 10 % compared with the current volume produced vehicle. The saving is split at a ratio of 70 to 30 in the utilization of technologies with optimized energy require-ments and the reduction of friction on contacts respectively. The CO2 demonstration vehicle was created on the basis of a current Porsche Cay-enne with a V8 engine, where Schaeffler de-signed and verified the individual components and Porsche was responsible for system adjust-ments and validation in the entire vehicle. Each measure was backed up by calculations and vari-ous experiments, and the overall reduction was verified in the vehicle model and in vehicle mea-surements.

Reducing the losses in the engine generated a re-ducti on in fuel consumpti on of 5.8 % in the NEDC. Modifying the valve control VarioCam Plus by means of electric camshaft phasing and an opti -mized switchable tappet on the intake side con-tributed to 4.1 % of this reducti on. The reduced fricti on power in the valve train, belt drive and chain drive by means of lightweight components and coat-ed engine components reduced the overall fuel consumpti on a further 1.7 %.

The tapered roller bearings in the front and rear axle fi nal drive units were re-placed by double row angular contact ball bearings thereby re-ducing the fuel con-sumpti on in the NEDC by a total of 1.1 %. Compared with con-venti onal volume pro-

duced units, the fricti on power was reduced by 42 % on the rear axle fi nal drive unit and 35 % on the front axle fi nal drive unit.

Using wheel bearings with opti mized fricti on char-acteristi cs and replacing the hydraulic roll stabilizer with an electric roll stabilizer reduced fuel con-sumpti on in the NEDC by 3.2 %. The reducti ons on the rolling test stand are already generated when traveling straight ahead by eliminati ng the drive power of the hydraulic pump, so that even higher savings can be expected during measurements in more customer-oriented vehicle tests on winding roads.

Further opti mizati ons to the chassis and drive train of the demonstrati on vehicle that were not previ-ously included in the measurements will be carried out during the next few months.

Collaborati on between Schaeffl er and PorscheToday, engineers of both companies are working closely on assessing and implementi ng ideas for developing new components while taking all the

appropriate steps right from the start. This is because this is the only means of taking on the challenge of a future that categori-cally and quickly re-quires lower contami-nant emissions, lower CO2 output and lower fuel consumpti on. This arti cle shows that this strategy can lead to very unconventi onal soluti ons. However, it cannot be overlooked in this very special case that progress can only be made in small steps in such a young and modern vehicle such as the Porsche Cayenne. Lowering the fuel consumpti on by around 10 % is the result of several, in some cases far-reaching, measures.

Together, these two companies carried out ad-vance development on new components that were tested in a demonstration vehicle based on the current Porsche Cayenne. The demon-stration vehicle is easily recognizable since it features the “Co2ncept-10 %” logo as well as pictures of the various new components it con-tains.

High-tech valve ti ming adjustment – electric camshaft phasing and opti mized valve lift acti vati onThe first step of the task was to demonstrate how the fuel consumption and CO2 emissions can be reduced in a V8 engine from a Porsche Cayenne by optimizing the already very success-

ful VarioCam Plus system. To do so, engineers at Schaeffler and Porsche replaced the hydraulic camshaft phasing system in volume production with an electric system. This solution involves very compact electric motors that adjust the timing of the valves on the intake and exhaust camshafts. The high torque required for this is due to the high power transmission ratio of the small electric motor that can reduce the speed by a ratio of 66:1 and, at the same time, increase the torque of the electric motor by the same ra-tio.

The electric system has two advantages com-pared with the conventional hydraulic solution:

• Less energy is required since the motors only operate when adjusti ng the valve ti ming is necessary. There are theoreti cally speaking also no longer any limits to the ti ming angle. In practi ce, this means that a larger ti ming angle can be used,

• as well as faster adjustment.

Both these improvements not only lower fuel con-sumpti on, the engine performance characteristi c of the engine is also improved.

Along with the valve ti mings, the valve lift on the intake side plays a decisive role in the energy-sav-ing plans of our engineers. The lift is adjusted by electro-hydraulic valve tappets. This eff ect that re-

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Figure 1 The demonstrati on vehicle

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for charge movement

Figure 2 Opti mized VarioCam Plus system





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duces both fuel consumpti on and emissions is gen-erated by two variable values:

• Less valve lift and shorter opening ti mes reduce the charge-exchange losses in the parti al load range and increase the speed of the incoming air for more eff ecti ve mixture preparati on.

• Furthermore, the system facilitates the deacti vati on of the intake port (to generate high charge movement) when the engine is operati ng in the lower parti al load range and varies the level at which both intake valves of each cylinder are opened when the engine is operati ng in the higher parti al load range.

These ingenious measures trigger a small “whirl-wind” in each combusti on chamber that permits the creati on of an especially homogenous and ig-nitable gasoline-air mixture that ensures very effi -cient combusti on cycles even at low loads.

The improvement generated by the opti mized Va-rioCam Plus system lies in the parti al load range (Figure 3). According to current results, adjusti ng the valve ti ming, valve lift and charge movement lower the fuel consumpti on calculated for the NEDC by 4.1 %.

A very informati ve diagram (Figure 4) shows the possible new designs for the valve tappet of the future. For example, the valve tappet of the future may no longer be round and similar to a cup, but may be shaped in such a way so that it only has

contact surfaces for the tappet where a certain functi on is fulfi lled.

Lowered fricti on power in the inter-nal drive systems of the engineThe diameter of tappets has significantly re-duced during the last decade and the new design has enabled us to reduce the moving mass to

only 30 %. For optimum smooth running, the cast camshafts and the tappets they actuate un-dergo intensive surface treatment. After intense development, the contact surfaces of these parts are now coated with TriondurC+, a DLC coating system that is around 3 μm thick and has a hardness of up to 3000 HV, which can signifi-cantly reduce friction and offers an ex-tremely high resis-tance to wear. Fur-thermore, the valves of the V8 engine of the future could be significantly lighter, despite not being any smaller in size.

This general reduction in moving masses not only promotes the running smoothness and lively revving abil-

ity of the engine, but also curbs the fuel con-sumption.

Here too, the fricti onal torques were clearly low-ered by more than 20 %.

Using similar fi ne tuning, our engineers also low-ered the required drive power for the chain drive that operates the four camshaft s. Chain tensioners opti mally adjusted to the drive and coati ng the chain sprockets also lower the fricti on.

The forces in the primary drive can be lowered by around 25 % if all changes to the primary drive and valve train are made simultaneously.

The V-belt drive on the front of engines has be-come more complex during development, since the desire for improvement and comfort has in-creased the number of units to be driven. This re-sults in increasing power expenditure that has to be compensated with targeted measures.

Porsche and Schaeffl er have taken on this chal-lenge and have found the soluti on for reducing losses in the presented project with a series of

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Figure 5 Reducti on in driving torque due to measures on the valve train

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Figure 4 Measures for the valve train

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Figure 6 Measures in the primary drive

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Figure 7 Reducing forces in the primary drive

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Figure 8 Measures in the ancillary drive





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measures. More eff ecti ve chain tensioners and the use of a narrower belt (six ribs instead of sev-en) facilitate the smooth transmission of power. Even the drive force requirements of the idler pul-leys were reduced by limiti ng the roller to one guide profi le.

A further important role is played by the overrun-ning alternator pulley in the eff orts to lower the required power for the belt drive. This is because it enables the generator to keep a near constant speed, despite irregular sti mulati on from the crank drive and valve train. The more constant speed of the generator reduces the dynamic forc-es in the belt drive and therefore the fricti on and power loss in the system. However, the potenti al for reducing losses is heavily dependent on the relevant applicati on and on the actual charging current of the generator, since high performance delivery produces a high braking torque in the generator. This, in turn, infl uences the dynamics in the belt drive.

The diagram clearly shows the level of fl uctua-ti ons in speed in the drive and therefore the forc-es in the belt drive of the generator in city traffi c without an overrunning alternator pulley. The mean of several very precise measurements tak-en in the NEDC when using an overrunning alter-nator pulley is a 0.3 % reducti on in fuel consump-

ti on. In additi on, reducing the load placed on the belt by means of the pulley can increase the life of the V-belt.

Measures on the front axle and rear axle fi nal drive units and wheel hubsWith its INA and FAG brands, the Schaeffl er Group is one of the world’s leading experts in rolling bearing technology. This is also one of the rea-sons why the Schaeffl er Group is a perfect devel-opment partner for Porsche when it comes to smooth running in vehicles. Schaeffl er then also pointed out that fricti on losses in the fi nal drive units on the front and rear axles can also be sig-nifi cantly reduced.

The recommended measures involve replacing the traditional tapered roller bearings on the universal shaft drive side with tandem ball bear-ings and more efficient single-row ball bearings on the left and right sides of the differential housing for driving the axle shafts.

The results are remarkable. The power loss on the front axle is reduced by 35 %. This increases to 42 % on the rear axle due to the increased load.

The Porsche Schaeffl er project also generated more improvements and smooth running in the wheel bearings.

In this case, improvements were made due to the opti mized preload of the double-row ball bearings and by redesigning the seal system including the outer seal. Together with a minimized bearing pre-load, the omission of garter spring load by means of a modern seal without steel springs as well as reducing the sealing interference led to a 30 % re-

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Figure 9 Improving fuel consumpti on and reducing forces by means of overrunning alternator pulleys -42 %

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Figure 11 Reducing power loss by means of an opti mized rear axle fi nal drive unit

Replacement of tapered rollerbearing by angular contact

ball bearing

Figure 10 Measures on the front and rear fi nal drives

Outside seal system

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Figure 12 Measures for wheel bearings

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Figure 13 Reducti on of torque loss with opti mized wheel bearings





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ducti on of fricti on losses with constant sealing ac-ti on.

Overall, the potenti al for reducing fuel consump-ti on is far below 1 %. Despite this fact, the energy effi ciency is generated by the sum of all individual measures and the opti mizati on of individual poten-ti al that seems low at fi rst glance is also worth-while.

Electrically adjustable roll stabilizersThe requirements placed on a sporty SUV such as the Porsche Cayenne are extremely varied. In road traffi c, the vehicle must master bends in the road without roll movement. Off road, this “taming” is not desired: Severe axle arti culati on ensures con-tact with the ground and tracti on. Up to now, Porsche has met this challenge with an acti ve hy-draulic control system for the stabilizers on both axles. However, due to the permanent supply of oil to the hydraulic pump, this soluti on requires per-manent operati on of the pump and therefore leads to permanent losses.

Experience has shown that some hydraulic sys-tems can be effi ciently replaced by electric sys-

tems. This knowledge generated a soluti on that sets the required stabilizer torques as needed. During this process, the electric motor only re-quires power when the pivot actuator turns and thereby generates torque. When maintaining torques, only the relati vely low electric resistance losses must be compensated for. The roll stabiliza-ti on system is relati vely inacti ve on a freshly laid motorway, but has to be considerably more acti ve

on a normal road de-pending on the condi-ti on of the road, the number of bends, and the driver’s driving style. This is why the electromechanical roll stabilizing system has an extremely large potenti al for savings compared with the un-controlled hydraulic system where the sup-ply of oil to the pump is constant.

Adjusti ng the roll stabi-lizers using the electri-cal system lowers the consumpti on in the NEDC by 3 %.

Taking stock of fuel consumpti on and emissions: 10 % reducti onFigure 16 shows the simulation model and the variety of factors that facilitate a reduction in fuel consumption. Before implementation, all measures were evaluated in prototypes and dur-ing experiments regarding their contribution to lowering fuel consumption using calculations in a vehicle model. Specific simulation models for individual road resistances are shown in the rel-

evant functional blocks along the drive train. During the project, the advance development tasks for the components were split between Schaeffler and Porsche, which meant that data and characteristic diagrams were determined on component test stands at Schaeffler, on fired en-gine test stands at Porsche and in vehicle tests that provided a physical representation of the function behavior of the components. This data was used to adjust the simulation program dur-ing the early stages of development, which made it possible to make statements about the influ-ence of each measure on fuel consumption. More detail was given to these statements dur-ing further steps of development.

The overall savings realized on an existing vol-ume production vehicle are currently around

10 % when all mea-sures are considered together. However, this is not the end of the line. Porsche and Schaeffler are using their growing experi-ence to reduce fuel consumption even further. 70 % of the improvements made so far involve technol-ogy with optimized energy requirements and 30 % involve re-ducing friction in the drive systems.

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Figure 14 Measures for roll stabilizati on

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Figure 17 Results of NEDC calculati on

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Figure 15 Reducing fuel consumpti on and drive power by means of opti mized roll stabilizati on





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The calculati ons made on the basis of measure-ments taken on test stands show that fuel con-sumpti on and consequently CO2 emissions could be reduced a further 10 % at the current stage of advance development. Here, opti mized valve con-trol has the lion’s share. It is also worth noti ng that the 3 % saving generated by the electrically con-trolled roll stabilizer will probably be even higher during normal day-to-day operati on that deviates from standardized test stand cycles. The counteref-fects of the measures with each other can infl u-ence the potenti al of single measures to reduce fuel consumpti on.

In additi on, Porsche and Schaeffl er will work inten-sively on successfully tapping further potenti al thereby reducing fuel consumpti on and CO2 emis-sions.

Safeguarding a re-ducti on in fuel con-sumpti on during vehicle tests

The next step involved fi tti ng the various com-ponents in a demon-strati on vehicle. Mea-surements on the road and on a rolling test stand were made with this vehicle to confi rm the calculated potenti al of the measures for cut-ti ng fuel consumpti on.

In order to evaluate the benefi t in relati on to the outlay, it is impor-tant to verify the po-tenti al of each measure in the vehicle itself. As

menti oned above, the bearings in the front and rear axle fi nal drives were replaced with opti mized bearings. The individual potenti al of these bearings was determined in coast down tests with volume producti on fi nal drive units and modifi ed fi nal drive units on a rolling test stand.

During these tests, the vehicle coasts down from a starti ng speed of 120 h/km to 5 h/km. A comparison between the opti mized rear axle fi nal drive unit and the volume produced unit shows that the coasti ng ti me is 2.5 % longer. Adjusti ng the rear axle fi nal drive unit road resistance functi onal block of the simulati on model using this result leads to a calcu-lated improvement in fuel consumpti on in the NEDC of around 1 %. This means that it was possible to confi rm the total reducti on in fuel consumpti on of 1.1 % for front and rear axle fi nal drive units previ-ously ascertained from component tests.

ConclusionTaking stock of this joint project between Porsche and Schaeffl er using the Cayenne opens up a wide range of possibiliti es for the future. The combina-ti on of the measures illustrated for minimizing losses shows that it is possible to reduce the fuel consumpti on of a conventi onal drive with a gaso-line engine in a two-digit percent range without hybridizati on. The soluti ons presented are not lim-ited to SUVs and can be transferred to other types of vehicles and drives.

Individual improvements such as the more smooth-running rolling bearings can easily be transferred to volume producti on. Other components must undergo a cost benefi t analysis to show whether volume producti on development can begin.

Figure 18 Measurements taken with the vehicle on the rolling test stand

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Beforeop�miza�on

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Calculated fuel consump�on reduc�on NEDCRoll out test comparison with/withoutop�mized rear axle gearbox

Figure 19 Results of measurements on the vehicle

new measures for reducing fricti on in the drive train · split at a ratio of 70 to 30 in the...

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